The invention relates to an air-cooled single cross flow cylinder head motorcycle internal-combustion engines having a crankshaft pointing in the driving direction of the motorcycle
ft. This camshaft controls overhead inlet and outlet
through rocker arms. The engine has a scavenging direction which is approximately aligned with respect to charge cycle devices in the cylinder head and encloses an acute angle .alpha., with the axis of rotation of the camshaft
An internal-combustion engine of this general construction is known in DE-A-No. 27 03 520. The engine therein is a flat twin engine having cross-flow cylinder heads and a camshaft arranged in each cylinder head in parallel to the crankshaft and pointing into the driving direction. Each cylinder-head comprises one inlet and outlet valve which are arranged in a plane which is in parallel to the crankshaft and rises toward the outside. The camshaft, which is in parallel to the respective valve plane, acts upon the valves through rocker arms. The inlet and outlet duct of each cylinder head is arranged relative to the respective valve plane in such a manner that a scavenging direction exists which falls from the rear top of the engine toward the front bottom and which encloses an acute angle with the axis of rotation of the camshaft.
The above-described arrangement requires a timing case which is essentially placed on the cylinder head and disadvantageously enlarges the overall dimensions of the flat twin engine and also results in a center of gravity of the internal-combustion engine which is located higher above the road surface.
Furthermore, a V-2 engine having cross-flow cylinder heads is known from Volume 31b of the Third Edition of "Mitteilungen des Institutes for Verbrennungskraftmaschinen und Thermodynamik" (Information of the Institute for Internal-Combustion Engines and Thermodynamics) of the Technical University of Graz from Illustrations 9.4T 2f-2g/II. The valves of this engine are arranged in planes which are essentially in parallel to the respective scavenging direction. However, here all the valves are actuated by a single camshaft, arranged between the cylinders in the engine power section, in parallel to the crankshaft. This requires a expensively constructed transmission. Here valve levers are actuated by the camshaft through relatively long push rods and rocker arms arranged in the cylinder heads for the control of the valves. Because of the relatively high oscillating masses and a high elasticity in the transmission, a precise valve control is hardly possible with acceptable expenditures. This results, in addition to unfavorable fuel consumption and exhaust values construction, in a machine with a reduced performance and rotational speed. Furthermore in this arrangement, considerable mechanical noise is created for an air-cooled engine and this also require relatively short servicing intervals for the valves due to the valve play changes.
It is the object of the invention to provide an internal-combustion engine of the above-mentioned construction, without the above-mentioned disadvantages. The invention allows for a relatively stiff valve control in a small installation space. Here several identical valves are arranged in an area of the cross-flow cylinder heads which is well-cooled by the air stream. This object is achieved by having inlet and outlet valves arranged in planes which are essentially in parallel with respect to the scavenging direction of the engine and with the valve camshaft in driving connection with the rocket arms through hollow tappets arranged in the cross-flow cylinder head.
An advantage of the invention is that the valve camshaft can be arranged at a minimum distance and next to the valve arrangement. It uses transmission elements of a small or short construction. Thus a stiff valve drive is achieved while, on the whole, the installation space is small and the arrangement is compact.
Here where the internal-combustion engine is constructed as a flat twin engine with cylinder heads which are cooled by an air stream, several outlet valves for each cylinder head may be advantageously arranged in areas which are cooled by the directly approaching air stream. Other developing possibilities of the valve arrangement are not significantly limited by the invention. For this reason, in a further development, a cross-flow cylinder head is therefore preferred which has four valves which are arranged overhead in a V-position. Here, a relatively small V-angle is preferred between the groups of identical valves for achieving a flat roof combustion chamber in the cylinder head. In addition, a centrally arranged spark plug may be provided in parallel to the cylinder axis.
In order to achieve a simple construction of a cross-flow cylinder head, a separate bearing bracket is provided as the support for the valve camshaft as well as for housing hollow tappets interacting with the shaft, so as to provide a driving connection with rocker arms which are also arranged at the bearing bracket. This bearing bracket, which is constructed as a single mounting unit, is held by means of a screwed connection with the cylinder head, the tension rods of which may also be fixed in the engine power section.
In order to reduce the overall height of the cross-flow cylinder head, a chamber is provided in the head, which is open on the cylinder-head cover side, for receiving the camshaft arranged overhead at the bearing bracket. A relatively narrow chamber is sufficient for the camshaft which is arranged at the bearing bracket in divided bearings. Further the valve camshaft may have a short construction. The short construction is promoted by an additional design of the cross-flow cylinder head, so that a driving device of the camshaft may also be housed in the chamber. Finally, it is advantageous to arrange the chamber in the area of the cylinder head which is predominantly on the engine inlet side, because stress to the enclosed valve gear caused by temperature will be reduced by the relatively cool area of the cylinder head.
The bearing bracket, which requires little installation space, for the above-described preferred 4-valve arrangement, has guides for the hollow tappets which are arranged between the parallel shafts of the rocker arms. As a result, the rocker arms have short and therefore stiff arms. These rocker arms have sliding surfaces which are constructed as cylinder surfaces to provide a perfect, low-wear and slidably movable connection with flat or slightly spherical faces of the straight hollow tappets.
Finally, within the scope of the invention, a bearing bracket is provided for a rocker shaft which is approximately in parallel to the scavenging direction and which can drive a 2-valve or 3-valve cross-flow cylinder head.
In a flat twin engine having a crankshaft pointing in the driving direction and having camshafts which are parallel to this crankshaft, the invention provides a scavenging direction which slopes down in driving direction with a preferred multiple outlet valve arrangement. The required pipe length for an exhaust system can be achieved by enclosing the cylinder partially in an actuated manner. The scavenging directions of both cylinder heads may, in addition, extend in planes which are essentially in parallel with respect to the longitudinal axis of the vehicle, or of the engine. Alternatively the planes can be sloped with respect to one another against the driving direction. As a result, the intake pipes which, according to the scavenging direction can extend in driving direction from the upward rear part of the engine toward the bottom front, may be placed advantageously with respect to sufficient leg room at the motorcycle by means of a spatially acute-angled arrangement of the scavenging device with respect to the camshaft
For the construction of the valve control, the common arrangement of the valve gear and the transmission elements (rocker arms and tappets) in a common bearing bracket is also advantageous. This bearing bracket results in a stiff, complete and space-saving OHV valve control. This permits small valve angles and a central spark plug position for an optimal combustion chamber. This has a favorable effect on the internal-combustion engine with respect to its performance, torque, elasticity, and to its noise, fuel consumption and exhaust quantity. Finally, the bearing bracket results in advantages during series assembling and simplifies the cross-flow cylinder head with respect to casting and manufacturing techniques.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.